Circuit interrupters



March 20, 1956 w EDWARDS ETAL 2,739,207

CIRCUIT INTERRUPTERS Filed Sept. 28, 1951 Insulation Ill/I/Il/l/ 8 3 O bH W Fig.3.

Insulation 44 Fig.2.

INVENTORS Andrew W. Edwards 8 Kenneth L. Niebouer- ATTORNEY UnitedStates Patent CIRCUIT ENTERRUPTERS Andrew W. Edwards, East lsicKeesport,and Kenneth L. Niebauer, Pittsburgh, Pa., assignors to WestinghouseElectric Corporation, East Pittsburgh, P23, 2: corporation ofPennsylvania Application September 25, 1951, Serial No. 248,724

3 Claims. (Cl. Mil -150) Our invention relates generally to circuitinterrupters, and it has reference in particular to circuit interruptersof the fluid filled type in which a flow of fluid is utilized inextinguishing an are drawn during a circuit interruption.

In circuit interrupters it is usually highly important to extiguish theare as rapidly as possible, so as to complete interruption of thecircuit. For this purpose many circuit interrupters have been providedwith various means for directing a flow of an arc extinguishing mediuminto the are for assisting in extinguishing it. In the main, theseinterrupters have utilized movable pistons actuated by the movingcontact for effecting the flow of an arc extinguishing fluid. This meansthat the arc will be established before any stream of fluid is directedfor extinguishing it. Delay is therefore involved before the arc can beextinguished.

It is therefore an object of our invention to provide for initiating aflow of arc extinguishing fluid in a circuit interrupter before an arcis drawn by the moving contact of the circuit interrupter.

Another object of our invention is to provide for effecting movement ofarc extinguishing fluid actuating means in a circuit interrupter beforean arc is drawn between the contacts of the interrupter.

Yet another object of our invention is to provide in an interrupter ofthe fuse type for preventing establishment of the main arc until a flowof arc extinguishing fluid for extinguishing it is initiated.

It is an important object of our invention to provide in an automaticreclosing circuit breaker for permitting the moving contact to have apredetermined amount of travel before separating from the stationarycontact, so

that a flow of arc extinguishing fluid may be first initiated.

These and other objects of this invention will become more apparent uponconsideration of the following detailed description of preferredembodiments thereof, when taken in connection with the attached drawing,in which:

Figure l is a substantially longitudinal sectional view of a circuitbreaker embodying one form of this invention, with most of the partswithin the circuit breaker casing being shown in elevation;

Fig.2 is an enlarged partial view of the contact struc- I ture such asmay be used with a circuit breaker similar to that of Fig. l, in adifferent embodiment of the invention; and

Fig. 3 is an enlarged view, broken away in part, of a fuse typeinterrupter embodying the invention in another of its forms.

This invention is disclosed in Fig. 1 as being embodied in a circuitbreaker of the type mounted in a metal tank or container 2 having anopen top, such as is disclosed in the copending application Serial No.162,174 of James M. Wallace et al, now Patent No. 2,647,184, issued July28, 1953. According to such disclosure, a cylindrical liner 4 isprovided for the side wall of tank 2, with a liner disk 6 being providedfor the bottom of tank 2. The liners 4 and 6 are preferably of aninsulating material, such, for example, as fiber or the like. The top oftank solenoid coil 20 therebetween.

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2 is adapted to be covered by a cover casting 8, which may be secured tothe tank in any desired manner, such, for example, as by bolts 9 (onlyone of which is shown). Cover casing 8 is adapted to support the circuitbreaker mechanism and contacts by means of a plurality of insulatingsupports 10 (only one shown) secured to integral lugs (not shown) on theunder side of the cover casting, and to a casting 14. Other supports 16of magnetic material are adapted to be connected to the supports 10 tosupport a plate 18 from casting 14 for mounting a Still other insulatingsupports 22' are adapted to be connected to the supports 16 to supportthe top cap 24 of an interrupter chamber 26 from plate 18.

The interrupter chamber 26 includes a cylinder 28 of insulatingmaterial, such as fiber, having threaded ends, one of which is threadedinto top cap 24, and the other end of which is threaded into a bottomcap 30. The bottom cap 30 of the interrupter chamber 26 has a centrallylocated tapped opening for receiving a contact supporting screw 32adapted to have a nut 36 on the outer end thereof for securing aconductor 38 thereto. In accordance with the teachings of our inventiona normally stationary contact head 34 may be slidably supported on thescrew 32, as by a stem 35 which passes axially through the screw 32, aspring 37 disposed about the stem beneath the head 34, and a stop pin 39which passes through the lower end of the stern for limiting movement ofthe contact head.

The conductor leads from contact screw 32 to a conductor located in oneterminal bushing (not shown) secured to cover casting 8. A movablecontact rod 44 has the lower end thereof extending through a centralopening in top cap 24 of the interrupting chamber, and is provided witha tubular sheath 46 of insulating material, such as fiber or a moldedinsulating material at the point where it passes through top cap 24. Thelower end of contact rod 44 has a contact head 48 for engagement withthe movable contact head 34 on stationary contact screw 32, in theclosed circuit position.

Within interrupting chamber 26 there is also provided a fluid directingstructure mounted on the lower end of contact rod 44, this structurecomprising a top plate 52 having a central opening slidably receivingthe lower end of contact rod 44, and a nozzle plate 54 having a centralopening somewhat larger than contact head 48, with these two platesbeing secured together by a plurality of connecting studs 69 which areshouldered to maintain plates 52 and 54 in spaced relation, and aresecured in place by screws 62. The fluid directing structure furtherincludes a valve plate 64 located between plates 52 and 54, and beingmovable between nozzle plate 54 and a stop defined by shoulders on studs60. The entire fluid directing structure is biased downwardly by a coilcompression spring 68 reacting between top plate 52 and the sheath 46 ofcontact rod 44, with this spring being in a compressed condition in theclosed circuit position due to nozzle plate 54 engaging a stop ring 69held in place between the lower end of cylinder 28 of the interruptingchamber and a shoulder on bottom cap 30. There is also a stop washer 70secured between contact head 48 and the lower end of the sheath 46 oncontact rod 44, to permit locating the plate 52 with a limited amount ofresilient lost motion, so as to insure its movement with the rod and yetpermit the plate to engage stop 69 without affecting engagement of thecontacts 48 and 34.

Bottom cap 36 of the interrupting chamber is provided with a pluralityof inlet openings 72 adapted to be controlled by a check valve or ring74 freely mounted for movement between bottom cap 30 and stop ring 69.The top cap 24 of the interrupting chamber is provided vwith a hollowchamber 76 having an opening at one side 6 as at '78, and alsocommunicating with the interior of the interrupting chamber as by outletopenings 80 provided in the inner wall of top cap 24. The outletopenings 80 are adapted to be controlled by a valve ring 82,-preferablybiased to a position away from openings '80 by a plurality of coilcompression springs 84 (only one of which is shown). I

The structure of interrupting chamber 26 and its operation is generallysimilar to that disclosed and'cla'irned in the copending application ofl. M. Wallace, Serial No. 542,681, filed June 29, 1944, on CircuitInterrupters, now Patent No. 2,528,197, issued October 41, 1950, andassigned to the same assignee as this invention. Accord ingly, referenceis hereby made to such copending application for a more detaileddescription of the construction and operation of this type ofinterrupting device. "in general, as described therein, when contact rod44 is moved upwardly, an arc will be struck a short time later betweenthe contact tips 34 and 48, and since the interrupting chamber is filledwith an arc extinguishing fluid such as oil, being submerged incontainer 2 which is filled with such fluid up to level L, the arc willdecompose the oil and generate gas within the interrupting chamber. Thiswill cause an internal pressure which'will seat valve rings 74 and 82 onthe inlet and outlet openings, respectively. This internal pressure willalso act on contact rod 44 and its sheath 46 in a piston-like mannor toaccelerate its movement away from fixed'contact screw 32. The fluiddirecting structure starts to move with initial upward movement ofcontact rod 44 because it is held in engagement with stop washer 70 byspring 68. Accordingly, as contact rod 44 moves upwardly the entirefluid directing structure including nozzle plate 54 will be pulledupwardly with the contact rod, and fluid will be forced from the upperpart of the interrupting chamber around the outer edge of plate 52- andthrough the central opening in nozzle plate 54 to provide a blast offluid through the contact region in a generally longitudinal direction.In accordance with the teachings of the present invention, the contacts34 and 48 will not immediately separate to initiate the arc. Instead,after contact rod 44 has moved upwardly an amount equal to the lostmotion of stem in screw 32, the moving contact 48 will separate from thecontact 34 and an arc will then'be drawn. The blast of fluid willalready have commenced, and will therefore be available to extinguishthe are drawn between the contact heads, whereupon the pressure withininterrupting chamber 26 will decrease and permit valve rin 82 to uncoveroutlet openings 80 andthus permit escape of gases from the interruptingchamber through outlet openings till, hollow chamber 76, and openings 73to be discharged at one side of the top cap 24 for the interruptingchamber. Gases which thus escape from the interrupting chamber arereplaced by fresh fluid flowing into the bottom of the interruptingchamber through inlet opening '72, which While the general displacesvalve ring 74 upwardly. structure and operation is thus very similar tothat disclosed in the above-mentioned copending application of I. M.Wallace, it will be observed that a major difference resides in themethod of initiating the flow of arc extinguishing fluid in theinterrupting chamber, due to the novel arrangement of the fluiddirecting structure and the stationary contact.

in order to automatically open the contacts in response to overloads onthe circuit, it will be observed that the movable contact rod isconnected by a conductor 86 to one terminal of solenoid coil 2% andthis, in turn, is connected by a conductor $8 to a terminal bushingwhich is secured on cover casting 3 by bolts 4-2. The solenoid coil 29is thus connected in series with the circuit through contact tips 34 and48. A solenoid core 90 in the form of a tube is slidably mounted oncontact rod 44, being of a magnetic material such as iron. The upper endof solenoid core 99 is slidably received in a collar 92 secured betweensupporting plate 18 and the bottom of the solenoid coil 23. The solenoidcoil is annular in form and has a central opening receiving adashpotsleeve 9a of insulating material, such as fiber or a moldedinsulating material. An actuating tube 96 of a non-magnetic materialsuch as brass or the like, has its lower end secured in the lower end ofsolenoid core 99 and it extends upwardly through solenoid coil 29, beingprovided with a collar $7 resting on the top surface of casting 14. Acoil compression spring 58 is received within actuating tube 96 andreacts at its lower end against a collar 9 secured in the lower end oftube 96 and at its upper end engages an abutment 9? on contact rod 4provided by the lower edge of an insulating rod 93 to which the rod 44is connected.

Casting 14' is also of a hollow construction with the hollow chamberltlt) formed within this casting communicating with the upper end ofdashpot sleeve 94, and'having an'opening at one side which may be closedby a plug 1&2. However, if desired, plug 102 may be removed and theopening from chamber lull will then be controlled by a piston valvemember 194 vertically slidably movable in a counting cylinder 1% mountedin casting 1d. The lower end of counting cylinder 1% is closed by a plughaving an opening controlled by a ball-check valve 108 to permit fluidto enter the lower end of the cylinder but preventing it from escapingtherefrom. I Piston valve 104 is provided with a stem 11% at its upperend which has a plurality of annular ratchet flanges 112 formed thereonin spaced relation with the bottom of an extension 113, for'engagementby a U-shaped pawl 11$ pivotally mounted as at 121 on a lever 116 havinga split outer end located at opposite sides of contact rod 44, andresting on collar 97 of actuating sleeve 96. Lever 116 is pivotallymounted on casting 114 at 117, and is normally biased clockwise to keepthe outer end in engagement with collar 97, by a coil tension spring 118secured between lever 116 and a lug integral with casting l4. Pawl 11-4is biased in a counterclockwise direction relative to lever 116 by aspring 120, to maintain the pawl in a position for engagement with thebottom of extension 113 and the flanges 112.

The particular construction or" casting 14 and parts associatedtherewith described above is similar to that disclosed and claimed inthe copending application of l. M. Wallace et al., Serial No. 719,524,filedDecember 31, 1946, on Circuit Interrupters, now Patent No.2,626,329, issued January 20, 1953, and assigned to the same assignee asthis invention. Accordingly, for a more complete disclosure of theconstruction and operation thereof, reference is hereby made to thiscopending application of J. M. Wallace et al. Generally speaking, theoperation of interrupting the circuit, when solenoid coil 20 becomesenergized sufliciently to move core 9%) upwardly, is that the core firstmoves upwardly displacing fluid in dashpot sleeve 94 upwardly intocasting 14, and if plug 102 is in place the fluid can escape only by wayof the relatively small clearance between core 98 and collar 92, so thatthe upward movement of the core will thus be slowed down by this dashpotaction. However, if plug 102 is not in place, the fluid will be freelydischarged from chamber 100 in casting 14, and solenoid core 99 will notbe restrained in its upward movement, at least on a first circuitinterrupting operation in any series of closely successive circuitinterrupting operations. Upward movement of core 9%, of course, carriesactuating sleeve 96 and its collar upwardly, and this moves lever 116upwardly to carry pawl 114 into engagement with the lower edge of theextension 113 on piston HM to carry the piston upwardly a predeterminedamount. Upward movement of core also will ultimately compress spring 9 5suiliciently forv the core to cause upward movement of contact rod 44,to thus establish an arc and interrupt the circuit in the mannerpreviously described. After a circuit interruption, core 90 and contactrod 44 are free to descend tofi gether to close the. circuit, exceptthat, it plug" 102 of casting 14 is in place, this descent will beslowed down by the necessity of replacing fluid within the upper part ofdashpot sleeve 94 through the relatively small clearance between thecore 90 and collar 92. If upon reclosing of the circuit breaker contactsthe overload still persists the contacts will immediately be reopened inthe same manner except that this time pawl 114 will engage the uppermostflange 112 and counting 104 will be advanced a further amount to aposition where it closes the opening from chamber so that the secondclosing'operation will be slowed down by the dashpot action of core 90in sleeve 94, even though plug 102 is not in place. On a third closelysuccessive circuit opening operation the upward movement or" core 90will be slowed down by the dashpot action of sleeve 94, even though plug102 is not in place, because piston valve 104will still be at a positionwhere it closes off the opening from chamber 100 of casting 14. Whilepiston 104 is biased by gravity to reset to its original position, thisaction is very slow due to the necessity of displacing fluid trappedbeneath the piston through the relatively small clearance between thepiston and cylinder 106, with the result that piston 104 does not havetime to reset where circuit interrupting operations occur in rapidsuccession.

The upper end 93 of contact rod 44 is connected by a pair of insulatinglinks 124, of fiber or the like, to the common pivot 126 of a pair oflinks 128 and 130. Link 130 is biased to the left as viewed in Fig. l bya coil tension spring 132 connecting link 130 and cover casting 8.However, since link 128, which is of inverted channel form having sideflanges, has its other end pivoted on a bracket 136 supported from covercasting 8 as by screws 138, and since link 130 has an integral hook 134'which extends through an opening in the bight portion of link 1 28, theresult is that spring 132 biases link 128 in a clockwise direction, tothus bias contact rod 44 downwardly to exert pressure causing pressureengagement of contact tips 48 and 34.

There is also provided within cover casting 8 a pair of toggle levers140 and 142 connected by a center pivot 144. Toggle lever 142 has itsother end mounted as by a pivot 141 which is secured in a U-shaped lever143 mounted in cover casting 8 by a pivot 148 and bracket 145, whiletoggle lever 140 is mounted on a fixed pivot 146 and extends out throughan opening in the cover casting beneath a hood portion 147 to form ahandle extension 152 having a hook-end 156 in the outer end thereof formanual operation. A coil compression spring 150 engages the bight oflever 143 and the casting 8, thus pushing this lever and center pivot144 to the left, so that at the position of the parts illustrated, withcenter pivot 144 located beneath a line extending from fixed pivot 146to pin 141, the handle extension 152 of lever 140 is maintained inengagement with a stop screw 154 beneath hood 147.

The spring arrangement and mechanism mounted within cover casting 8 isidentical with that disclosed in the copending application of H. L.Rawlins et al., Serial No. 7l9,572, filed December 31, 1946, on CircuitInterrupters, now Patent No. 2,622,167, issued December 16, 1952, andassigned to the same assignee as this invention. Accordingly, for a morecomplete description of the structure and operation of these parts,reference is hereby made to the Rawlins et al. application. In general,the operation of these parts during a circuit opening operation is suchthat initial upward movement of contact rod 44 during a circuit openingoperation results in levers 128 and 130 approaching each other to thusreduce the force component of spring 132 which biases contact rod 44downwardly, until the end of spring 132 connected to lever 130substantially coincides with the pivot mounting of lever 128 on bracket136. At this time, spring 132 will have substantially no force componentin a downward direction, and accordingly, contact rod 44 is not opposedby spring 132 in its further upward movement. It will be apparent thatwhen the circuit is interrupted, thus freeing contact rod 44 fordownward movement, which may or may not be impeded by the dashpot actionof solenoid core in dashpot sleeve 94 as previously pointed out, thatthe parts will move downward initially due to the force of gravity,until the point is reached where links 128 and begin to separate, andthus establish a downward component of spring 132, to accordinglyincrease the speed at which final engagement of the contacts occurs and,of course, finally establish a contact pressure, as previously pointedout.

Handle extension 152 of toggle lever may, of course, be moved downwardlyto move center pivot 144 upwardly overcenter, to thus release spring150. The lever 143 has a transverse pin 153 which extends beneath theadjacent end of lever 130, so that upward movement of this center pincarries link 130 with it, and consequently, raises contact rod 44 toopen the circuit breaker contacts. Such manual opening of the circuitbreaker contacts is, of course, accelerated by spring as soon as pivot144 passes overcenter, and the circuit breaker conta ts are maintainedopen by spring 150. After such a manual operation the circuit breakermay be manually closed by moving handle extension 152 upwardly, and thuspermitting contact rod 44 to move downwardly in the manner previouslydescribed.

Toggle lever 1.42 is provided with an extension 158 which overliesextension 113 of insulating material, such as fiber or a moldedinsulating material, mounted on the upper end of stem 110 of piston 104.The purpose of this is to lock the circuit breaker contacts open after apredetermined number of closely successive circuit interruptingoperations have occurred. Thus, as previously pointed out, piston 104will be advanced a predetermined amount on each circuit openingoperation, and if these operations occur in close succession, the pistonwill eventually be advanced an amount sufiicient to cause its extension113 to engage extension 158 of toggle lever 142, and move pivot 144overcenter, to thus cause opening of the'contacts by spring 150 in themanner previously described, and this spring, of course, will then holdthe contacts at an open circuit position.

instead of utilizing a spring-biased stationary contact such as shown inFig. 1, the stationary contact may, as shown in Pig. 2, comprise acontact head 34 having a stem 35 extending through the screw 32, andprovided with a stop pin similar to the pin 39 of Fig. 1. In place of aspring 34, the stem 35 may have a collar 161 of a permanent magnetmaterial such as one of the well known aluminum nickel alloys. Thecontact rod 44 may be provided with a contact stud bolt 162 at its end,having a magnetic sleeve 163 of iron or the like disposed thereon.Whenever the contact rod 44 is raised, the stationary contact 34 willfollow because of the attraction of the magnet 161 for the sleeve 163,until the stop 39 prevents further movement of contact 34, whereupon thecontacts separate. This initial movement of contact 34 permits thenozzle structure to initiate the flow of a stream of arc extinguishingfluid before an arc is drawn between the contacts to provide for morerapid extinction of said arc.

Referring to Fig. 3, the reference numeral 164 denotes generally acircuit interrupter of the fuse type, comprising a tubular housing orcontainer 166 of insulating material such as fiber, glass, or the like,having metal caps 167 and 168 secured to opposite ends. The lower cap168 is cup-shaped and has an axially projecting internal boss 170 towhich one end of a flexible shunt 172 is fastened, and is provided witha flange 173 to which one end of a tension spring 174 may be secured.

The upper cap 167 may comprise a substantially open cylinder and have aninternal shoulder 176 for supporting a removable plate 177 having acentral opening 178 for receiving the stem of a stationary terminal orcontact member 179 which is secured in the opening by means of .a collar1S0 threaded thereon. A cover 181 may be utilized to close the upper endof the cap 167, being secured to the cap, as by a press fit of a flange182 about the periphery of the cap.

A movable main arcing contact 183 is normally connected to the stern ofthe stationary contact member 179 by a fusible link element 134 and astrain element 185,

as for example, by solder or the like. The contact 183 has a hexagonalhead 186 disposed to be threadably se cured to a terminal member 187 atthe upper end of the shunt 172. The terminal member 187 has a flange 18$suitably mounted thereon, to which the other end of the tension spring174 is secured, for applying a predetermined tension to the strainelement 185. v

In order to direct aflow of arc extinguishing fluid such as a gas-likesulphur hexafluoride, or oil, with which the casing 166 may besubstantially filled, a nozzle piston 193 may be secured to the movingarcing contact 183 so as to move therewith. The piston may comprise acupshaped member having a central opening 189 for receiving the arcingcontact member 183, and a plurality of openings 19%) for directing fluidthrough a reduced annular orifice 192 into the path of an are betweenthe contacts.

For the purpose of initiating flow of the arc extinguishing fluid beforethe main arc .is drawn between the moving contact 183 and the stationarycontact 179, means such as the arc tube 194 may be provided, forproviding a circuit connection between the contacts 179 and 183 when thefuse element 184 and strain element 185 blow, for a predeterminedmovement of contact 183. This tubemay comprise adjacent conductivetubular members 195 and 196 disposed axially of the contact 183 andterminal 1'79, and separated by an annular air gap 197, which issufliciently short that it will break down while the moving contact 183is still in contact with the member 1%. The member 195 may be secured tothe lower side of plate 177 by being mounted on the head .191 ofstationary terminal member 179, .while the member 196 may be slidablydisposed about and in contact with the upper end of the moving contact183. Means such as the insulating sleeve 19% of fiber or the like may bethreadably or otherwise secured to the members 195 and 196 tomechanically connect them and maintain them in predetermined spacedrelation.

Accordingly, when the fusible element 184 is melted by a current inexcess of the value for which it is designed, the strain element-135,which is of a high strength material, such as a nickel-chromium alloy,and has a relatively high resistance, melts almost immediately,releasing the moving arc contact 183. The con-tact 183 is thereuponactuated by the spring 174 and the nozzle piston 193 moves therewith todirect a stream of arc extinguishing fluid through the annular orifice192 about the moving contact 183. The gap 197 flashes over as soon asthe fuse element 184 and strain element 185 melt, since it has abreakdown value below that of the voltage impressed thereon when thefuse and strain element melt, and the moving contact 183 remainselectrically connected to the stationary terminal 179 by the arc acrossthe gap, until the moving contact reaches the end of the lower section196 of arc tube 1%. A main arc is thereupon drawn between the movingcontact 183 and the lower end of the arc tube 19%. Since this arc isimmediately in the path of the stream of arc extinguishing fluid fromthe nozzle 193, it is immediately extinguished, and as the are betweenthe sections 195. and 196 of the arc tube is in series circuit relationtherewith, it becomes extinguished also.

It is believed apparent from the foregoing that this invention providesan arrangement for circuit interrupters, whereby a stream of arcextinguishing fluid employed in the interrupter is utilized toextinguish an arc drawn Having described -a preferred embodiment of theinvert-'- tion, in accordance with the patent statutes, it is desiredthat the invention be not limited to the particular constructionsdescribed herein, inasmuch as it will be apparent to persons skilled inthe art that many changes and modifications may be made intheseparticular constructions'without departing from the broad spiritand scope of the invention. Thus, it is apparent that the invention neednot be employed with circuit breakers of the automatic reclosing type,although it has certain novel features of cooperation with this type ofcircuit breaker, but may be employed in any typeof circuit breaker orinterrupter where an arc extinguishing fluid is employed. Accordingly,it is desired that the invention be interpreted as broadly as possibleand be limited only as required by the prior art.

We claim as our invention:

1. In a circuit interrupter, separable contacts, an arc chamberenclosing said contacts, electroresponsive means operable in response toa predetermined value of current through said contacts to effectseparation of said con tacts, means movable in said chamber with one ofsaid contacts in a piston-like manner for directing a stream of arcextinguishing fluid in the region of said contacts, and lost motionmeans for permitting the other one of said contacts to move apredetermined distance in contact with said one contact to permit saidstream to be established before said contacts separate.

2. A circuit interrupter comprising, a container for an arcextinguishing fluid, separable contacts disposed in said container, anarc chamber surrounding said contacts, electroresponsive means connectedin series with said contacts for moving at least one of said contactsfor separating them in response to a predetermined value of current,means for reclosing said contacts following a separation, a movablepiston structure disposed in the arc chamber adjacent and movable withsaid movable one of said contacts for directing a stream of the fluid toextinguish an arc between the contacts, and means including a lostmotion mounting for the other of said contacts and means for biasing itto follow said movable one of the contacts to prevent separation of thecontacts until the stream is established.

3. In a circuit interrupter, a container for an are extinguishing fluid,a substantially closed arc chamber in said container, separable contactsdisposed in the chamber in said fluid, a movable contact rod foractuating one of said contacts, electroresponsive means including asolenoid connected in series with said contacts and an armature operablein response to a predetermined value of current for actuating said rodto separate said contacts, means biasing said contacts togetherfollowing a separation, means including an axial stem and spring meansfor biasing the other of said contacts for predetermined movement withsaid movable contact, and fluid pump means comprising a piston in thechamber operable immediately upon movement of said movable contact todirect a stream of fluid for extinguishing an are between said contacts.

References Cited in the file of this patent UNITED STATES PATENTS1,966,901 McMahoh July 17, 1934 2,061,301 Duffing Nov. 17, 19362,095,441 Howe Oct. 12, 1937 2,442,477 Wallace et al. June 1, 19482,551,772 Thibaudat May 8, 1951

